There are various known systems and methods that attempt to create homogeneous distribution of an average temperature inside solids requiring relatively long thermal development (TD) times. Examples of such processes include annealing of solids to remove stresses and thermal development of glass materials and crystal materials to fix recorded Bragg Gratings (BGs), e.g., distribution of refractive index modulation. In the latter case, an additional requirement to the process is the conservation of the sample flatness. Deviations from the original shape result in the variation of the angle of beam incidence on the Bragg grating and in the impairment of total diffraction efficiency. Conventional industrial furnaces are limited to providing a temperature gradient of about one degree Celsius in a relatively restricted volume. In addition, such furnaces do not allow measurement of sample shape conservation. Thermal development of glass samples with homogeneously recorded gratings in such furnaces results in significant degradation of plane surfaces of samples and in relatively low total diffraction efficiency of Bragg gratings even in the case of medium-sized samples—about 25 mm×25 mm.
Most known techniques for long time homogeneous thermal development of solids are based on usage of specialized furnaces with small temperature gradients in a heat chamber. Furnaces with relatively small volume heat chambers provide smaller temperature gradients. Therefore, such furnaces are usually considered for high homogeneous thermal development. Additional equipment placed in a heat chamber results in a volume increase and temperature gradient.